It has been known to use a fluid jet, typically a water jet, discharged at high pressure from a nozzle, for the machining, especially the cutting, of work pieces. The jet diameter is typically in the order of around 1 mm. In the case of so-called “abrasive water-jet cutting” (AWJ), water pressures of more than 300 MPa are used to generate a water jet with abrasive particles. Such a water jet can be used as an omni-directional cutting tool for cutting wide range of metallic and non-metallic materials with thicknesses of up to 200 mm.
In large turbines, particularly steam turbines, blades can be for example attached to the rotor by means of a pinned blade root where press-fitted or interference-fitted pins are placed in boreholes extending through the blade root and the rotor. Prior to their placement in the boreholes, the pins are for example cooled to low temperatures, e.g. by means of liquid nitrogen. Thus slightly reduced in size, they are then pressed into the borehole with heavy-duty tools, which results in a tight, high-tension fit between the pin and the turbine rotor and blade root.
During turbine maintenance, the turbine blading must be removed and replaced requiring the removal of the press-fit pins from their boreholes. However, this is a difficult procedure as the space between the blade rows can be confined, in some cases to dimensions as narrow as 15 mm (in case of industrial steam turbines)
The co-owned U.S. Pat. No. 7,628,678 describes the in-situ use of a water jet tool having a nozzle that is arranged at an angle with respect to a main body of the water jet tool. The water jet is directed over a portion of the surface of the pin and removes that portion thereby fragmenting the pin. In order to minimise damage to the surrounding material, the portions removed touches the interface between the pin and the surrounding solid material at a minimal number of points and over a minimal extent of the interface.
Compact collecting devices for water jets have already been proposed, which can be moved together with the water jet tool and can also be used in the case of confined space conditions at the application site. Such devices are described for example in the published European patent applications nos. EP 0244966 A2 and EP 0252657 A2 and the co-owned published United States patent application no. US 2009/0178526 A1, incorporated herein by reference for general aspects of using and controlling an impact baffle. The '526 application shows a collecting device for detecting the first impact of the high pressure water jet upon the collecting device, and using a corresponding signal for controlling the use of the water-jet tool, or detecting a malfunction of the collecting device and using a corresponding signal is used for terminating the use of the water-jet tool.
In view of the known prior art, it is seen as an object of the invention to improve the known collecting device, particularly for very confined spaces.